The present invention relates to valve stem seals, and more particularly to a two-piece valve stem seal preferably for use in an internal combustion engine, but applicable to other valve stem sealing applications.
The primary function of a valve stem steal in an internal combustion engine, for example, is to allow adequate lubrication at the valve stem/valve guide interface while minimizing internal oil consumption. Valve stem seals of this general type are known in the prior art, as shown in U.S. Pat. Nos. 5,558,056; 4,947,811; 4,909,202; 3,554,562; and 3,554,180, for example. In addition, a two-piece valve stem seal of this general type is shown in U.S. Pat. No. 5,775,284, which is assigned to the same assignee as the present application and which has overlapping inventorship with the present invention.
A valve stem seal assembly generally includes a rigid shell structure and a seal body, with the assembly having a generally hollow interior adapted to receive a valve stem guide. Typically the shell structure supports the shell body, which surrounds the valve stem in order to essentially “meter” the provision of oil for lubricating the valve guide's inner diameter and the outer diameter of the valve stem. At the same time, however, the valve stem seal serves to minimize the amount of oil that can be drawn into the combustion chamber to pass to the engine's exhaust. If the rigid shell is not properly located in relation to the valve guide, the sealing element might not properly seat upon the valve stem thus causing non-uniform pressures at the cylinder and valve guide, undesirable wear patterns on the seal or valve stem and unpredictable lubrication of the valve stem and valve guide.
Some prior art valve stem seals have had histories of cracked flanges during vehicle operations due to shock waves and internal stresses at the flange portion of the valve stem seal. Some of such prior art valve stem seals also have not had sufficiently flat flange portions, thus further increasing the likelihood of flange cracking.
In addition some prior art two-piece valve stem seal assemblies have been difficult to assemble by their manufacturers, as well as presenting further difficulties to consequent manufacturers assembling the finished valve stem seal assembly into an engine or other device using such assemblies.
These problems sometimes have resulted from the need to assemble or insert the “upper” generally cylindrical shell portion of the vale stem seal assembly “upwardly” into the “lower” generally cylindrical shell portion from the “bottom” of the lower shell portion, i.e., from the end of the lower shell portion that bears against the engine's cylinder head or other such member of a device through which the valve stem extends. This difficulty sometimes results from the “upper”, end portion of the lower shell portion having a relatively small bearing surface (against which the insertion forces are directed) when compared to the bearing surface at the lower end of the lower shell portion.
With regard to the consequent manufacturer's assembly of the finished valve stem seal assembly into an engine or other device, the vigorous nature of various automated parts feeding and assembling apparatus can sometimes cause two-piece valve stem seal assemblies to separate during such operations. This of course can cause malfunction, or at least temporarily halt or slow down, such consequent assembly operations.
Although the two-piece valve stem seal assembly described and claimed in the above-mentioned U.S. Pat. No. 5,775,284 performs well and successfully overcomes various short-comings of the prior art, the present invention seeks to further improve upon that design and overcome these and other disadvantages of the prior art.
Other objectives of the present invention are: to provide a valve stem seal which will offer greater resistance to the forces exerted by the valve spring which causes the flange to crack; to prevent the sealing member of the assembly from separating from the valve guide; and to provide a flanged valve stem seal that will not rotate about the valve guide due to the rotational motion of the valve spring, thus minimizing torsional stresses on the valve's return spring and reducing wear.